1. Field of the Invention
The present invention relates to processes related to the manufacture of above the knee and below the knee prosthetic sockets using aerospace quality fibers, resins, and textile braiding techniques to produce lighter weight, stronger, lower cost prosthetic products relative to conventional production methods.
2. Description of the Prior Art
Currently, production of trans-tibial and trans-femoral prosthetic sockets starts with the creation of a cast of the patient's residual limb using plaster of Paris wraps or bandages to map the shape of the residual limb. After the wrap has hardened, it is carefully removed and is used as a mold for the casting of a positive plaster mold, a replica of the residual limb, with a pipe embedded in the mold in the axial direction to facilitate handling. After the mold has set, the plaster wrap or bandage is removed.
The plaster mold or cast can be modified by the prosthetics technician, known as a prosthetist, by adding or subtracting material based on the prosthetist's knowledge and experience of the residual limb and its distinctive characteristics in terms of the locations of soft tissue, muscle, and bone. This process of modification is referred to as rectification. The prosthetist uses the cast rectification to produce a better distribution of interface pressures between the socket and the residual limb during usage.
The positive plaster cast is then used as a mandrel or positive form in order to create a negatively formed socket. At this point in the process, a sheet of thermoforming material like polystyrene or PETG is heated until flexible, then drawn over the positive mold, taking care to push the thermoform material into the contours of mold such that the thermoform is a negative replica of the residual limb. The outer surface is then lightly sanded in order to maximize the bonding of subsequent material additions.
Alternatively, instead of casting a positive plaster replica of the limb in the hardened plaster wrap or bandage taken from the patient, some fabrication facilities create a digitized solid model computer file by scanning the inside of the patient's plaster wrap with a mechanical sensor or laser scanner. This digitized image can then be modified by computer software designed for this purpose to dimensionally add or subtract “material” from the digitized image in a manner similar to that of a prosthetist adding or shaving material off the plaster cast to adjust or fine tune the cast to better replicate the truncated limb.
Once the Computer Aided Design (CAD) file is generated, it can then be loaded into computer controlled CNC machine tool often referred to as a “carver”, which cuts out a replica of the residual limb in a rigid but malleable material like a high density polymeric foam. At this point, like the process described above for a plaster cast, a thermoforming material is drawn over the positive mold making a negative replica of the limb.
Prior to the formation of the socket, whether from a wax, plaster or high density foam mold, an attachment or adaptor plate is adhered to the bottom or distal end of the thermoset covered mold using an adhesive or harden able putty such as Bondo to secure the plate to the mold, and fill in voids around the plate and the thermoset covered mold. This plate is used to secure the pylon which is essentially a pipe that secures the prosthetic foot to the socket that is fitted to the residual limb, or, in the case of the above the knee socket, attachment to a mechanical knee joint. This attachment plate has a groove around its circumference and in some embodiments, metal straps that can be used to anchor the attachment plate to the materials that form the socket.
The next step in the conventional production process is to secure fabrics (graphite cloth or fiberglass weave) at the distal end of the socket, securing the cloth with wire or other material in the groove of the adaptor plate. The cloth is then added up in several layers around the mold, with a stretchable material drawn over the outside to secure the cloth or weave prior to introduction of a resin matrix material.
The next part of the process involves a Vacuum Assisted Resin Transfer Mold (VARTM) process where a vacuum bag secured around the exterior of the mold with cloth layup contains the resin which is poured into the top of the composite assembly and manually “massaged” down the socket assembly to assure the cloth laminate is fully wetted. After the resin is cured, the plaster has to be chipped out of the socket and interior and exterior surfaces cleaned prior to use. This conventional process suffers from a number of drawbacks. One, the wrap-casting process is somewhat messy and labor intensive as are many of the subsequent steps in the formation of the socket. Secondly, if the prosthetist does not make a digitized solid model of the limb, there is not a permanent record of either the initial plaster wrap representing the shape of the residual limb, or the subsequent negative plaster mold, or, more importantly, the rectified plaster mold, since it has to be broken out the mold to complete the production of the socket. Since there is no record of the shape of the residual limb, the whole process has to be repeated if a socket is damaged or lost, or needs minor adjustments later.
The need exists for improved methods and structures for making prosthetic sockets.